This disclosure relates to steering systems for motor vehicles, and, more particularly, to a steering damping device that utilizes a magneto-rheological fluid to controllably dampen vibratory motion.
Vibration is an oscillatory motion about an equilibrium point. If the oscillatory motion is the result of a forcing function that is applied once and then removed, the oscillatory motion is known as natural or free vibration. However, if a forcing function is applied repeatedly to a system, the motion is known as forced vibration. Such forced vibration may be periodic, impulse, stepped, or random in nature.
Vibration within a motor vehicle is almost always forced vibration. Impulse-type forced vibrations typically result from the movement of the motor vehicle over a road surface, which almost always includes some degree of irregularity therein to cause a jarring motion to the motor vehicle. Such jarring motion is known as xe2x80x9croadfeelxe2x80x9d and is typically transferred from the road surface through the steerable wheels and through the steering system and chassis of the motor vehicle to a steering device such as a hand steering wheel where it is experienced by an operator of the motor vehicle. The forced vibrations may also be the result of the normal operation of the engine of the motor vehicle and its accessory drive systems, which typically causes oscillatory motion of the motor vehicle that is periodic in nature.
Typical methods of compensating for the forced vibrations transmitted to the operator include conventionally structured shock absorbing devices and/or variation of the xe2x80x9cstiffnessxe2x80x9d of components associated with the shock absorbing devices. These devices can include a liquid disposed therein in order to effectuate viscous damping of the vibrations. The devices comprise the suspension system of the motor vehicle and are most often mounted between the steerable wheels and the chassis to damp the vibration that results from movement of the motor vehicle across the road surface, thereby effectively buffering the operator and passengers of the motor vehicle from roadfeel. Such devices generally provide a constant damping force that may be exceeded by excessive vibration, which typically results when the motor vehicle encounters potholes or other extreme variations in the road surface. Regardless of the magnitude of the disturbing force causing the vibration, some level of comfort is generally afforded to all of the occupants of the motor vehicle. However, because the operator almost always has both of his hands on a steering device having direct mechanical communication with the steerable wheels through the steering system, and because the steering system is generally not damped, the operator experiences roadfeel that may not be otherwise experienced by the passengers.
A vibration damping system for a motor vehicle and a method of damping vibrations resulting from roadfeel using magneto-rheological fluid to selectively dampen vibratory motion are disclosed herein. A linear vibration damping system includes a piston slideably disposed within a cylinder, a magneto-rheological fluid disposed within the cylinder, and a magnet disposed in magnetic communication with the magneto-rheological fluid. The magnet is typically an electromagnet that is variably controllable to provide control of the magneto-rheological fluid at the individual particle level. The cylinder may be mounted to the chassis of the motor vehicle, and the piston may be mounted to the steering system of the motor vehicle. The variable control of the magneto-rheological fluid may be effectuated through a controller configured to generate a signal that corresponds to a vibration sensed by the steering system. The generated signal may ultimately effectuate a change in the magneto-rheological fluid such that a frequency of the vibration sensed by the steering system is substantially equal to a frequency of the signal from the controller.
A rotary vibration damping system includes a cylinder having a steering shaft extending therethrough. A magneto-rheological fluid is disposed between an inner surface of the cylinder and an outer surface of the steering shaft. A magnet, which may be an electromagnet that is variably controllable, is disposed in magnetic communication with the magneto-rheological fluid. The magnet is controllable to provide variable control of the magneto-rheological fluid. The control of the magnet may be in response to a signal generated from a controller. The generated signal may ultimately effectuate a change in the magneto-rheological fluid such that a frequency of the vibration sensed by the steering system is substantially equal to a frequency of the signal from the controller.
A method of damping vibrations in a motor vehicle includes disposing a magneto-rheological fluid at a source of vibration in the motor vehicle, controlling the magneto-rheological fluid to effectuate a structural change in the magneto-rheological fluid, and subjecting the magneto-rheological fluid to a vibration from the source of the vibration. The control of the magneto-rheological fluid may include applying an electromotive force to a magnet disposed proximate the magneto-rheological fluid and forming magnetizable particles of the magneto-rheological fluid into fibrous structures that impart Bingham plastic Theological behavior to the magneto-rheological fluid.